Will Summertime Kill COVID-19? Here's What We Know

As spring weather surfaces the U.S., I can tell many of my friends and family are starting to go a bit stir-crazy. I wrote last week in Retirement Millionaire about how to remain calm in the face of this crisis.

One question that's on everyone's mind: As temperatures start climbing here in the U.S., will it be enough to slow the spread of COVID-19?

The short answer is yes. But the longer answer is that it won't stop the virus. At least, not by itself.

You might have seen many headlines suggesting that warmer weather will stop the spread of the virus... But there are just as many headlines saying that summer won't save us.

Making things even more tense: A committee from the National Academies of Sciences, Engineering, and Medicine released a paper this week on the subject. What they do well is summarize all of the current research on COVID-19. Much of it indicates that temperature and humidity do, in fact, slow the virus spread.

But they caution that we can't at this time expect the virus to slow down or stop in the coming months, regardless of temperature.

In this barrage of news, I wanted to take a hard look at what we know, what we don't know, and what we can realistically expect in the coming weeks and months.

First, there are several studies out there looking at temperature and humidity. Let's focus on the big ones...

One study released in mid-March came from the Massachusetts Institute of Technology. The researchers there saw that the majority of COVID-19 cases happened in the Northern Hemisphere, which is just ending the winter season. Places with temperatures between 37.4 and 62.6 degrees Fahrenheit have seen the highest rates of infection.

More important, the analysis highlighted this finding: Places with warmer climates (including the Southern Hemisphere, which is just ending its summer) had comparatively few coronavirus cases. In fact, they make up just 6% of total worldwide cases.

A study from the University of Maryland also modeled patterns of temperature, humidity, and latitude for the virus. It found that the biggest outbreaks have occurred in the band of 30 to 50 degrees north. That's the Northern Hemisphere strip that includes parts of China, South Korea, most of the U.S., and Europe. This band corresponds to similar temperatures.

The idea is that as the Southern Hemisphere starts to lower to these temperatures this fall, they'll start to see a similar rapid spread.

A study recently published in the Lancet Microbe showed that the virus responded to changes in temperature. As the temperature increased, the length of time until the virus was "undetectable" shortened. In other words, we can get rid of the virus with higher temperatures.

A lot of this comes down to the type of virus. Coronaviruses have a protective membrane around them (hence, the "corona" in their name). That membrane in most coronaviruses can't stand up to higher temperatures. Note, that's most, not all. So far, we're hopeful that COVID-19 follows this path as well.

A March study out of Beijing demonstrated that for every 1-degree increase in temperature and 1% increase in humidity, the virus had a slight drop in transmission. In other words, the warmer and more humid, the less easily the virus is passed from person to person.

That sounds great, right? Summertime should slow down the virus.

But all these studies come with some serious caveats (those nuances I mentioned at the beginning). For example, that Maryland study pointing out that the majority of cases occur in the 30-to-50-degree band... That band includes a good portion of the world's population. (Check out the population density map, here.) In other words, we can't say if the high numbers of cases are due to temperature and not population density and increased contact.

The problem we face today is that the research struggles to keep pace with the spread of this deadly disease. But that doesn't mean these early studies are wrong. Personally, I do think the warmer weather will help. But it's not the only thing we can hang our hopes on...

Temperature is just one factor that will stop this virus. The other factors are ones I've already urged you to follow in the Health & Wealth Bulletin.

We know we can change our behavior to avoid transmission. Social distancing, wearing masks in public areas, and washing our hands are all good ways to stay safe.

As for our immune systems, we need to get enough vitamin D to keep them healthy. Get out and get some sun – just be sure to keep a safe distance of at least six feet from other folks. Eat plenty of foods with vitamin C as well, like citrus foods and leafy greens.

Finally, as the number of hosts drops, the virus will stop spreading. This means that the virus will slow as it becomes harder to find a host (a human in this case) that hasn't already gotten infected and built up an immunity. As that number drops, so will the pandemic.

My takeaway from all of this is that we're scrambling to get solid research and data. It's difficult for research to keep pace with a rapid public health crisis. However, what we have so far is hopeful – we could see a drop soon with summer approaching. But it's important to keep practicing good preventive habits in the meantime. It won't just be the weather that will stop this pandemic – it depends on our actions, too.

What We're Reading...

Here's to our health, wealth, and a great retirement,

Dr. David Eifrig and the Health & Wealth Bulletin Research Team
April 16, 2020